Polycarbonate resin compositions and blends with other thermoplastic resins are widely used because of their excellent properties.
There have been many attempts in the art to provide polyorganosiloxane-based graft polymers which may be useful as impact strength modifiers for thermoplastic resins. See, for example, U.S. Pat. No. 2,891,920 (J. F. Hyde, et al.); and O. Graiver, et al., Rubber Chem. Tech., 56 (5), 918 (1983).
U.S. Pat. No. 3,898,300 states that a polyorganosiloxane-based graft copolymer for improving the impact strength of styrene (S)/acrylonitrile (AN) resin is formed by grafting S/AN comonomers in an emulsion system onto the vinylsiloxane or allylsiloxane containing silicone substrate. U.S. Pat. No. 4,071,577 describes a similar approach by using a mercaptosiloxane in place of vinyl-group containing siloxanes. European Patent Application No. 0,166,900 reports further improvement of polysiloxane-based graft polymers and increased S/AN impact strength by using acryloxy-functionalized siloxane as the graft-linking agent.
Relevant for its broad teachings is BASF's U.K. Patent No. 1,590,549 which describes the use of a polyorganosiloxane-based graft copolymer in various thermoplastic compositions. Poor compatibility is observed with these compositions. Similarly, European Patent Application No. 249,364 describes the use of a polyorganosiloxane-based graft copolymer in polycarbonate resin compositions and mixtures thereof with a saturated polyester and/or a polyester elastomer. The modifier therein has relatively poor rubber integrity and incompatibility with the resins as well.
The use of a diene or acrylic rubber-based modifier in thermoplastic resins has become a common practice in the art. The selection of either material depends largely on the end use purposes such as weatherability or low temperature impact resistance. Uniform color appearance of molded parts is a benefit which is gained by using a diene-based modifier over acrylics. However, the unsaturated moieties of the diene rubber restrict its outdoor use to some extent due to its tendency to oxidize and to yellow.
None of the references disclose the in-situ co-homopolymerization of vinyl monomers in the presence of siloxanes in an emulsion system, as described hereinbelow. The present invention is also directed to the use of graft polymers provided by subsequent graft polymerization of vinyl monomers (e.g. polymethyl (meth)acrylate, polystyrene or styrene/acrylonitrile copolymer) in the presence of such a co-homopolymerized polyorganosiloxane/vinyl-based substrate.
Surprisingly, it has been found that partial replacement of the oxidation or ozone sensitive rubber by a silicone-based rubber affects more improvements, such as low temperature ductility, low gloss, and impact and discoloring resistance against thermal aging on the blends described hereinafter. Unexpectedly, it is now possible to prepare low gloss polycarbonate and polyester blends having both excellent low temperature resistance and discoloration resistance by the addition of an effective amount of a silicone-based impact modifier to a diene-based modifier.
Mention is also made to European Patent Application No. 0,260,558 which discloses a combination of a silicone-based modifier with an alkylacrylate-based modifier. The patentee, however, makes no mention of the use of a diene-based impact modifier.
Additionally, it is described in S. Y. Hobbs et al, Polymer Bulletin, 17, 341 (1987) and S. Y. Hobbs et al, Journal of Material Science, 23, 1219 (1988) that in polycarbonate/saturated polyester resin blends, typical core-shell type modifiers such as Acryloid.RTM. KM-330 (polybutylacrylate core-methyl methacrylate shell, Rohm and Haas Company) or KM-653 (polybutadiene core-styrene/methyl methacrylate polymer shell, Rohm and Haas Company) segregate completely in the polycarbonate phase leaving the less ductile saturated polyester phase without any modifier.
There is evidence that in blends or mixtures comprised of two different resins, modification of both phases can significantly improve low temperature toughness. Van der Meer, in Dutch Patent Application No. 8600166 filed on Jan. 12, 1986 and in European Patent Application No. 0.236,596, published on Sept. 16, 1987, and Van der Meer and Hobbs in commonly owned copending U.S. Patent Application Serial No. 07/007,268 filed on Jan. 27, 1987, attorney's docket no. 335-2019 (8CB-10,306) have demonstrated this in polyphenylene ether (PPE)/polyamide (nylon) blends where Kraton.RTM. rubber (styrene-butadiene-styrene ABA block copolymer, Shell Chemical Company) was used to modify the PPE phase and maleic anhydride functionalized EPDM (ethylene-propylene-nonconjugated diene monomer polymer) rubber was used to modify the nylon phase.
BASF's German Patent No. 3521956 discloses the modification of the poly(butylene terephthalate) (PBT) phase of a PBT/PC polyphasic blend through the incorporation of olefin polymers that contain epoxy groups. The effectiveness of this method, however, depends on the ability to establish sufficient grafting of PBT on the epoxy groups of the olefin polymers during compounding in an extruder. The fact that both mixing and grafting chemistry must take place simultaneously places high demands on the compounding process, and therefore, the success of the BASF method has been limited.
It has been surprisingly found that migration of multi-stage graft polymer modifiers can be induced to segregate different modifiers into the different phases of polyphasic PC/PBT containing blends or mixtures of the same with poly(etherester) elastomer, poly(etherimide ester) elastomer and/or polyphenylene ether resins by varying the amount of (meth)acrylonitrile in the outermost stage of the modifiers. Therefore, two or more different modifiers, each with a different amount of (meth)acrylonitrile in the outermost stage can be combined to yield a desired distribution of modifier in the PC phase and in the PBT phase resulting in optimum toughness of the polyphasic blend. Such blends particularly exhibit superior low temperature toughness when compared with those formulated with modifiers residing in only one phase of the blend.